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Biased Fuses

Discussion in 'General Electronics' started by KellyClarksonTV, Jul 7, 2004.

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  1. Are there fuses around that are biased to blow when current runs one way rather
    than the other? If so, they could be used in non-rechargeable batteries, so if
    anyone tries to recharge one, the fuse will blow and disconnect the battery
    terminals alltogether.
  2. Ben Moss

    Ben Moss Guest

    I have often seen Zener or avalanche diodes in circuits to protect
    against excessive voltage spikes. The diodes are across the power
    terminals such that they will only conduct if + and - are flipped.
    The reverse-breakdown voltage of the diode is higher than the power
    supply voltage, so they will conduct if high voltages are seen,
    protecting the sensitive electronics. Additionally, if the power is
    hooked up to the circuit in the wrong direction, the diodes will
    conduct and prevent current from flowing the wrong direction through
    critical components.

    What you are describing could be implemented with a diode and a fuse,
    assuming the diode can handle the current. I think it would be better
    to make a "smart" battery charger that senses when the batteries are
    put in backwards and refuses to charge them. It could sense the
    existing voltage from the battery (even a dead battey should have a
    small amount), and if it's negative, have a bit of logic that would
    cut the power and flash the big red warning LED. I bet it could be
    done with an op-amp and a transisor (or less, if you're clever?). I
    don't know much about batteries, but I assume that if they go
    negative, then they have serious internal issues... A battery that
    dead would probably suck a lot of juice anyway.

    Hope that helps.
  3. SumGie

    SumGie Guest

    Um, really, you've been reading to much "Battlefield Earth!"

    Step away from the science fiction!

    And stop worrying about recharging the wrong kind of batteries! All you
    need to know is whether the ones you are charging are rechargeable. If they
    aren't, stop trying to recharge them. It doesn't take all that much in the
    way of brains to figure this one out, fer cryin' out loud. I can hardly
    believe that this question is STILL being asked, over and over again, in
    this forum. This has been going on for months now. What, do you think the
    answer will change if you ask enough times? (Stalks off while muttering
    imprecations and gesturing wildly...)
  4. Yea ... when I was a kid (6 or 7), I used to compulsively worry about putting
    the wrong batteries in the charger. I would check the charger evey 20 minutes
    even though I already saw they were rechargeable ... but today I kind of like
    doing it.
  5. Fred Stevens

    Fred Stevens Guest

    That's quite enough about batteries now - I'm sure everyone is tired of it!
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